Process for the production of lubricating oil



Patented Jan. 22, 1935 UNITED STATES PATENT OFFICE PROCESS FOR THE PRODUCTION OF LUBRICATING OIL No Drawing. Application October 30, 1933 Serial No. 695,957

11 Claims. (01'. 196-13) This invention relates to a process for the treatment of petroleum. More specifically it relates to a process for the treatment of petroleum with selective solvents.

In the production of lubricating oil for internal combustion motors it is highly desirable to obtain a product which exhibits a low temperature viscosity susceptibility, a low Conradson carbon value, a high stability towards sunlight and a low oxidation value. Crude lubricating oil fractions produced either as distillates or as residues are usually composed of mixtures of paraflinic, naphthenic, aromatic and olei'lnic hydrocarbons. The olefinic hydrocarbons are highly unsaturated and their presence in the finished lubricating oil is undesirable because of their unstable characteristics. These compounds are unstable and usually darken when exposed to sunlight. Furthermore, they have a high tendency towards polymerization with the result, after a considerable period, that these compounds are converted into resinous substances which increase the sludge value of the oil.

The aromatic and naphthenic hydrocarbons present in crude lubricating oil fractions are undesirable because of their high temperature viscosity susceptibility. These compounds exhibit too great a change in viscosity for a given change in temperature. The paraflinic hydrocarbons present in crude lubricating oil fractions are the most desirable materials to be employed as lubricants. These compounds are highly saturated hence, from a chemical standpoint, they are rather inactive and do not exhibit a tendency towards the formation of undesirable resinous or sludge forming constituents. Furthermore, these compounds exhibit a low temperature viscosity susceptibility. In other words, they exhibit a minimum change in viscosity for a given change in temperature. Furthermore, these highly saturated hydrocarbons are relatively stable to sunlight, undergoing little change in color on exposure. When I use the term parafilnic hydrocarbons I means those compounds which are present in petroleum/ having the aforementioned characteristics and which are liquid at ordinary temperatures. This group of hydrocarbons does not include those compounds present which are usually solid or semi-solid at ordinary temperature and which are known as wax or petrolatum.

In the production of lubricating oil from crude petroleum residues or distillates, it is becoming conventional in the art to separate the desirable parafiinic hydrocarbons from the undesirable olefinic, naphthenic and/or aromatic compounds by the use of solvents which selectively dissolve the undesirable hydrocarbons present in the petroleum fraction but which exhibit only a very limited solvent power on the desirable parafllnic hydrocarbons.

As a matter of convenience hereafter, I will refer to the desirable lubricating oil constituents of petroleum as the paraflinic hydrocarbons and to the undesirable constituents, such as olefinic, naphthenic and/or aromatic hydrocarbons as the non-parafiinic constituents of petroleum.

A number of selective solvents have been found desirable to separate the paraffinic from the non-. paraflinic hydrocarbons, for example, it has been shown that such materials as sulphur dioxide, beta beta dichlorethyl ether, chloranlline, nitrobenzene, aniline and furfural are highly selective as solvents for the non-paraflinic hydrocarbons. The foregoing selective solvents are relatively heavy as compared to petroleum. When these relatively heavy solvents are commingled with petroleum or petroleum fractions under the proper conditions of temperature, the undesirable non-parafiinic hydrocarbons present pass into solution to a greater or less extent but the desirable paraflinic hydrocarbons remain largely undissolved. If the commingled mass is allowed to remain in a quiescent state the solution of undesirable hydrocarbons settles to the bottom of the container and forms what is known as an "extract phase. The relatively light paraninic hydrocarbons rise to the top of the vessel and form a raifinate phase. These phases are then readily separableby ordinary deeantation means. The raffinate phase is usually found to contain a small quantity of the selective solvent and the extract phase ordinarily contains a relatively large quantity of the solvent. These fractions may be purified by subjecting them to distillation whereby the' solvent is distilled away from the hydrocarbon oils.

The conventional method of separating the undesirable non-paraffinic hydrocarbons from a hydrocarbon mixture consists in treating this mixture with a selective solvent under the proper conditions of temperature by the addition of sumcient solvent tdthe oil to remove the major portion of these undesirable hydrocarbons. Where one portion of the selective solvent is insufllcient to remove the major portion of the undesirable hydrocarbon present the method of treatment may be modified and the oil may be successively treated several times by the addition of fresh solvent to thepartially treated oil until a highly refined oil is obtained which is relatively free from the undesirable hydrocarbons. For example, an oil may be treated with liquid sulphur dioxide at a temperature of about 10 F. and the raffinate so obtained may be successively treated with sulphur dioxide at the same temperature until the major portion of non-paraffinic hydrocarbons have been extracted from the oil. The major portion of the undesirable hydrocarbons are usually removed by the first treatment with the selective solvent and the remaining undesirable hydrocarbons are then removed to a greater or less extent by the successive treatments.

It has also been proposed to regulate the solvent power of the extracting agent at any stage of the treatment in accordance with the solubility of the material to be extracted and as the refining of the stock by extraction progresses in a step-wise manner the solvent power of the treating agent should be increased.

By substantially increasing the solvent power or case of miscibility of the treating agent, it is possible to fractionate the raffinate, obtained after extraction with the pure solvent, into a further extract of lower solubility than the first extract obtained by the use of said pure solvent and a second raffinate of consequently still lower solubility than the first rafiinate.

It has been found desirable to first extract a hydrocarbon mixture with a pure selective solvent, such as aniline, nitrobenzol, sulphur dioxide, furfural, dichlorethyl ether or chloraniline and then re-treat the rafiinate so produced with a modified solvent, or with the same solvent at a higher temperature. As modifying agents such materials as carbon bisulphide, xylene, benzene, toluene, carbon tetrachloride, ethers or tetrachlorethane, may be employed.

By these processes the oil feed is divided in one general operation into three or more fractions of different viscosity-gravity constants.

The viscosity-gravity constant referred to in this application has been determined by the method employed by Hill and Coates set forth in the Journal of Industrial and Engineering Chemistry, Vol. 20, page 641 of 1928. This constant represents the paraifinicity or naphthenicity of an oil. A high value represents a high degree of naphthenicity while low values indicate relatively greater parafiinicity. Lubricating oils from natural crudes range from 0.903 viscosity-gravity constant for an extreme Gulf Coast type to 0.807 for an extreme Pennsylvania type, or even beyond.

For example, in a two stage extraction of lubricating oil using selective solvents, the first stage results in a primary raflinate and a low quality extract. To produce a high quality raffinate from the primary raffinate, the latter is again extracted, with the same or a different selective solvent than that first employed. As previously stated, this second extraction may be in the presence of a modifying agent described above. Another rafiinate and extract are produced from the primary rafiinate, resulting in a high quality raflinate and an intermediate grade extract. The high quality raflinate can be further purified, if desired, by further successive extractions and each of these successive extractions results in an intermediate grade extract.

I have found that in a solvent extraction process involving these successive extractions some of the lighter, less viscous lubricating oils having low viscosity-gravity constants are present in the intermediate grade extract rather than in the high quality rafilnate as desired. I believe that these valuable fractions are present in the intermediate extrac s instead of in the high quality raflinate because the oils of lower molecular weight or lower viscosity tend to be somewhat more soluble than fractions of higher molecular weight or higher viscosities having the same viscosity-gravity constant. The loss of high grade fractions in the intermediate grade extracts is undesirable.

It is an object of my invention to conserve the high grade fractions in the raflinate produced by extracting mineral oils by selective solvents.

It is a further object of my invention to extract a hydrocarbon mixture with a selective solvent and thereafter re-extract the raflinate so produced with a selective solvent which may or may not contain a modifying agent, and to recover from the intermediate grade extracts the valuable lighter, less viscous lubricating oils having desirable low viscosity-gravity constants.

I have found that these objects may be accomplished by subjecting the intermediate grade extract to distillation so as to divide it into fractions of varying viscosity. The lighter fractions which are vaporized and separately condensed comprise the valuable, less viscous lubricating oils of low viscosity-gravity constants which would otherwise be lost in the intermediate extract.

On fractionation of the intermediate grade extract by distillation; the lower viscosity-gravity constant for the lighter fractions is ordinarily not so low that the light fractions may be mixed directly with the high grade raffinate although in some cases this may be done. I usually introduce the above mentioned recovered light fractions into the feed stage of a continuous .countercurrent extractor wherein the selective solvent is introduced at an upper part of the extractor while the oil to be treated is introduced at a lower point. In some cases it is desirable to introduce said recovered light fractions above or below the point of introduction of fresh oil. This recovered material characterized by relatively low viscosity-gravity constant may be mingled with the primary rafllnate for re-extraction in the presence of the selective solvent and the modifying agent.

As an example of my invention in operating on a feed stock having a wide range of molecular weights, I may use a de-asphaltized and dewaxed Kettleman Hills long residuum, having a gravity of 18.9 A. P. I. at 60 F., a Saybolt Universal viscosity of 97 seconds at 210 F., and a viscositygravity constant of 0.873. The dewaxed long residuum was extracted in countercurrent equipment with 200 volume percent. of sulphur dioxide at 115 F. and the railinate so produced was then re-extracted in countercurrent equipment with 250 voume percent. of a mixture of 70% liquid sulphur dioxide and 30% benzene at 90 F. The rafiinate produced by the re-extraction with the sulphur dioxide-benzene mixture had a gravity of 26.6 A. P. I. at 60 F., 8. Saybolt Universal viscosity of 86.5 seconds at 210 F., and a viscosity-gravity constant of 0.817. The intermediate extract produced by the SOz-benzene extraction having a gravity of 19.1 A. P. 1., a Saybolt Universal viscosity of 102 seconds at 210 F., and a viscosity-gravity constant of 0.873 was th ensubjected to a fire and steam distillation and overhead fractions were obtained having the following characteristics:

Cut 1, gravity 26.7 A. P. 1., Saybolt Universal viscosity, 140 seconds at 100 F., and a viscositygravity constant of 0.849.

Cut 2, gravity 253 A. P. I., Saybolt Universal viscosity, 204.5 seconds at 100 F., and a viscositygravity constant of 0.853.

Cut 3, gravity 24.0 A. P. I., Saybolt Universal viscosity, 311 seconds at 100 F., and a viscositygravity constant of 0.857. The bottoms which remained after the removal of the three cuts had the foilowing characteristics:

Gravity 17.3" A. P. 1., Saybolt Universal viscosity, 216 seconds at 210 F., and a viscosity-gravity constant of 0.875. The cuts were produced as aerial condensate and represented 7.1, 8.4, and 8.6% by volume of the intermediate extract.

On comparing the viscosity-gravity constants of the three cuts with the viscosity-gravity constant of the material before distillation and the bottoms from the distillation, it is evident that the cuts are of considerably lower viscosity-gravity constant, indicating the presence in them of appreciable proportions of high grade oil which preferably should be in the first grade oil rafflnate rather than in intermediate grade extract. In practice, therefore, the second grade oil such as the intermediate extract is subjected to distillation and a yield of distillate taken of approximately one-third of the charge to the still. This distillate is then condensed and returned to the extraction equipment either with the original feed or preferably with the feed to the second stage of operation, in which the raffinate from the first stage is extracted with the sulphur dioxide-benzene mixture. In this way these light fractions are subjected to a further extraction operation and the desirable constituents are to a considerable extent recovered in the form of first grade oil raflinate, thus increasing the yield of the latter material.

When no effort is made to recover the valua-j ble products from the intermediate extract the yields in the foregoing example are as follows: high grade raffinate, 29.6%; intermediate grade extract, 45.4%; low grade extract produced by the primary extraction with liquid sulphur dioxide, 25.0%. However, when about one-third of the intermediate extract is vaporized, separately condensed and returned to the primary ramnate for reextraotion with the liquid sulphur dioxide and benzol mixture, the yield of high grade rafiinate may be increased from 29.6% to 34.3% with a corresponding reduction in the yield of intermediate grade extract.

It is to be understood that the foregoing is merely illustrative of one method of carrying out my invention and that many variations may be made by those skilled in the art within the scope of my invention which I claim:

I claim:

1. A process for the separation of paraifinic and non-paraffinic hydrocarbons from an oil containing the same which comprises extracting said oil in an extraction stage with a selective solvent, separating an extract fraction soluble in said selective solvent from a raffinate fraction insoluble therein, distilling said extract fraction to produce a light, viscous oil fraction having a lower viscosity gravity constant than the remaining extract fraction, and passing said distilled fraction to said extraction stage.

2. A process for the separation of parafiinic and non-paraflinic hydrocarbons from an oil containing the same which comprises extracting said oil in an extraction stage with a selective solvent, separating an extract fraction soluble in said selective solvent from a raflinate fraction insoluble therein, distilling said extract fraction to produce a light, less viscous oil fraction having a lower viscosity gravity constant than the remaining extract fraction, passing said distilled fraction to said extraction zone and withdrawing a rafflnate fraction from said extraction stage.

3. A process for the production of parafiinic and non-parafiinic hydrocarbons from oil containing the same which comprises extracting an oil in an extraction stage with a selective solvent and a modifying agent, separating an extract fraction soluble in said selective solvent and modifying agent from a raflinate fraction in-' soluble therein, distilling said extract fraction to produce a light, less viscous oil fraction having a lower viscosity gravity constant than the remaining extract fraction and passing said-distilled fraction to said extraction stage.

4. A process as in claim 1 in which said extract fraction is fractionally distilled to produce said light, less viscous oil fraction.

5. A process for the separation of parafiinic and non-paraffinic"hydrocarbons from a petroleum fraction containing the same which comprises extracting said oil with a. selective solvent, separating the extracted fraction soluble in said selective solvent from the rafiinate fraction insoluble therein, extracting said raffinate with a selective solvent to produce a high grade railinate insoluble in said solvent and an intermediate grade extract soluble therein, separating said high grade raflinate from said intermediate grade extract, distilling light, less viscous lubricating oil having low viscosity gravity constant from said intermediate grade extract and mingling said light, less viscous lubricating oil with oil passing to'the first mentioned extraction.

6. A process for the separation of paraflinic and non-parafiinic hydrocarbons from a petroleum fraction containing the same which comprises extracting said oil with a selective solvent, separating the extracted fraction soluble in said selective solvent from the raffinate fraction insoluble therein, extracting said rafilnate with a selective solvent to produce a high grade raflinate insoluble in said solvent and an intermediate grade extract soluble therein, separating said high grade rafiinate from said intermediate grade extract, distilling light, less viscous lubricating oil having low viscosity gravity constant from said intermediate grade extract and mingling said light, less viscous lubricating oil with oil passing to a previous extraction stage.

7. A process for the separation of paraflinic and non-parafiinic hydrocarbons from a petroleum fraction containing the same which comprises extracting said oil with a selective solvent, separating the extracted fraction soluble in said selective solvent from the rafiinate fraction insoluble therein, extracting said rafilnate with a selective solvent to produce a high grade rafllnate insoluble in said solvent and an intermediate grade extract soluble therein, separating said high grade raflinate from said intermediate grade extract, distilling light, less viscous lubricating prises extracting said oil with a selective solvent, separating the extracted fraction soluble in said selective solvent from the raflinate fraction msoluble therein, extracting said rafllnate with a selective solvent to produce a high grade raflinate insoluble in said solvent and an intermediate grade extract soluble therein, separating said high grade raifflnate from said intermediate grade extract, fractionally distilling said intermediate grade extract to vaporize light, less viscous lubricating oil having low viscosity gravity constant, separately condensing said light, less viscous oil and mingling said light, less viscous lubricating oil with oil passing to the first mentioned extraction.

9. A process for the separation of paraflinic and non-paraflinic hydrocarbons from a petroleum fraction containing the same which comprises extracting said oil with a selective solvent, separating the extracted fraction soluble in said selective solvent from the raiiinate fraction insoluble therein, extracting said rafllnate with a selective solvent to produce a high grade raflinate insoluble in said solvent and an intermediate grade extract soluble therein, separating said high grade raflinate from said intermediate grade extract,fractionally distilling said intermediate grade extract to vaporize light, less viscous lubricating oil having low viscosity gravity constant, separately condensing said light, less viscous oil and mingling said light, less viscous lubricating oil with oil passing to a previous extraction stage.

10. A process for the separation of paraflinic and non-paraflinic hydrocarbons from a petroleum fraction containing the same which comprises extracting said oil with a selective solvent, separating the extracted traction soluble in said selective solvent from the ramnate fraction insoluble therein, extracting said rafllnate with a selective solvent and modifying agent to produce a high grade raflinate insoluble in said solvent and modifying agent and an intermediate grade extract soluble therein, separating said high grade rafiinate from said intermediate grade extract, fractionally distilling said intermediate grade extract to vaporize light, less viscous lubricating oil having low viscosity gravity constant, separately condensing said light, less viscous oil and mingling said light, less viscous lubricating oil with oil passing to the first mentioned extraction.

11. A process for the separation of parailinic and non-paraflinic hydrocarbons from a petroleum fraction containing the same which comprises extracting said oil with a selective solvent, separating the extracted fraction soluble in said selective solvent from the rafflnate fraction insoluble therein, extracting said rafflnate with a selective solvent and a modifying agent to produce a high grade rafflnate insoluble in said solvent and modifying agent and an intermediate grade extract soluble therein, separating said high grade raflinate from said intermediate grade extract, fractionally distilling said intermediate grade extract to vaporize light, less viscous lubricating oil having low viscosity gravity constant, separately condensing said light, less viscous fraction and mingling said light, less viscous lubricating oil with oil passing to a previous extraction stage.

DAVID R. MERRILL. 

